Abstract: An instrument primarily adapted for use in photothermal keratoplasty procedures to shrink collagen tissue within a cornea of an eye being treated by controlled heating of the tissue with infra-red radiation. In a specific implementation example, a moveable multi-faceted prism is a primary optical element that forms a desired treatment infra-red radiation pattern from a single beam source. Multiple exposures to variations of the radiation pattern are provided. Parameters of two or more exposures to spot radiation patterns are stored in a memory of the instrument, and automatically configure the instrument to deliver the two or more exposures in sequence. Automatic calibration of the radiation intensity is also provided. A guide positions the head of the patient with respect to the instrument, and sensors monitoring movement of both the head and eye provide signals used to by the instrument to control radiation delivery.